The unlicensed usage of TV white spaces has been introduced by the Federal Communications Commission (FCC) as a means to supply bandwidth for the ever increasing demand for high quality communication and multimedia streaming using mobile devices. Utilizing “white spaces”, which refer to portions of the UHF spectrum (and parts of the VHF spectrum in the US), is only allowed while strictly forbidding interference with spectrum incumbents (i.e. TV receivers and wireless microphones). The ruling ensures the mitigation of interference between spectrum incumbents and White Space Devices (WSDs—devices intended to use the available bandwidth) through forcing WSDs to use one of two methods.
Following the first method, WSDs use white spaces after sensing the spectrum for TV transmissions with a very low threshold of −107 dbm. Spectrum sensing capabilities adds complexity and cost complications to WSDs so as to be able to detect this low threshold. The second method relies on consulting geo-location databases that keep track of available white spaces in certain areas. The main spectrum incumbents that need protection are TV receivers, not transmitters. TV receivers are typically passive, i.e. they do not transmit signals, and thus are difficult to detect. Therefore, geo-location databases protect TV receivers by protecting the entire coverage area of a TV transmitter. This is accomplished by keeping a record of information regarding TV transmitters, including location, antenna height, transmission power, and channels used. Geo-location databases combine this information with sophisticated propagation models to determine the protected area for a TV transmitter, where no WSD can be active.
It can be argued that current geo-location database regulations, while guaranteeing high protection of the spectrum incumbents, waste significant spectrum opportunities by protecting the entire coverage area of TV transmitters. In particular, it is not necessary true that the entire coverage area contains active TV receivers. In many cases, there are spectrum holes, both temporal and spatial, that are void of active TV receivers. These spectrum holes are wasted opportunities that can reach up to 23 channels in some urban areas (e.g. New York County, N.Y. and Miami City, Fla.) according to results presented herein. This gain is a great incentive for exploiting the potential for leveraging dynamic real-time TV white space awareness, especially in spectrum-hungry urban areas that will experience exponential demand for wireless bandwidth.
FIG. 1 summarizes the different scenarios in which white space opportunities are missed. In Scenario 1 is a temporally wasted opportunity. Although the white space network lies within the TV station's protected service area, the TV set in the vicinity of the network is turned OFF (or for the same practical purpose, currently running one channel leaving other channels available for unlicensed usage). Conventional geo-location databases that are not aware of the location of TV sets or their state, will declare the entire set of allocated channels in the area as unavailable.
The second Scenario is composed of two different instances (2.a and 2.b) in which white spaces are spatially wasted. In Scenario 2.a, the white space network lies within the protected service area but has no TV sets in the vicinity of the network. In Scenario 2.b, the white space network lies in the theoretical protected service area of the TV station, but the station's signal is obstructed. These scenarios lead to wasted white space opportunities, because conventional geo-location databases rely solely on propagation models.
Avoiding wasting spectrum opportunities is particularly important in urban areas, where huge numbers of wireless devices and congested RF spectrum are the norm. Table 1 shows the available white spaces for both fixed and portable WSDs in four urban and four rural cities. We observe that white spaces are more available for portable WSDs compared to fixed WSDs as the maximum allowable transmission power is 4 W for fixed WSDs and 40 mW for portable WSDs.
TABLE 1Urban and rural areas channel availability.AvailableAvailableAvailableChannels forChannels forChannels forPortablePortableCityFixed WSD (4W)100 mW WSD40 mW WSDUrban AreasLos Angeles, CA000New York, NY001Miami, FL002Philadelphia, PA103Rural AreasHudson, NY13718Palatka, FL151120Amador City, CA181020Conconully, WA231625
Temporal spectrum opportunity waste occurs when the state of the TV set (ON/OFF or the channel it is currently tuned to) is ignored. However, spatial spectrum opportunity waste occurs when an area with no TV sets, or outside the coverage area of a TV tower, is falsely protected, to over-protect TV receivers. These wasted opportunities are critical, especially in spectrum-hungry urban areas. From a different perspective, WSDs with spectrum sensing capabilities could partially avoid wasting spectrum. However, sensing capabilities are no longer a requirement, and equipping all WSDs with these capabilities will incur cost and power consumption issues.
Based on the aforementioned observations on current geo-location databases, a new cloud-based architecture for future dynamic real-time TV white space awareness that takes into account both TV transmitters and TV receivers is described. This invention builds on collaborative spectrum sensing approaches, focusing on maintaining accuracy on a city-wide scale. In particular, there is an argument for a crowd-sourcing approach, where hybrid devices collaborate to detect the state of TV receivers (e.g. location, ON/OFF, and TV station viewed) in their general area and the coverage of TV transmitters areas in real-time. Recent studies show that, while average Americans watch 5.2 hours of TV a day, less than 10% of these TV viewers watch broadcast channels. This information highlights the dynamic nature of spectrum opportunities that are constantly changing with each flip of a channel. Finally, it's possible to make use of the scalability and vast computational and storage capabilities of the cloud to keep track of these highly-dynamic, real-time and fine-grained TV white spaces.